Uranium recovry

ABSTRACT

Provided is a process for recovering uranium comprising
         (a) bringing a solution (I) into contact with a resin (I) to produce a mixture of a solution (II) and a resin (II), wherein the solution (I) is an aqueous solution that comprises 30 to 200 g/L sulfuric acid and that comprises 1 g/L to 50 g/L uranium, and wherein the resin (I) is a strong acid cation exchange resin, and   (b) separating the solution (II) from the resin (II).

The process of extracting uranium from ore often involves leaching the ore with sulfuric acid to produce an acid leach solution. Often, the acid leach solution is then passed through an ion exchange resin (for example a strong base anion exchange resin). The uranium is thought to become loaded onto the resin in the form of the [UO₂(SO₄)₃]⁴⁻ complex anion. Often the uranium is removed from the resin by eluting with sulfuric acid. The sulfuric acid eluate produced in this elution is an acidic aqueous solution that contains sulfuric acid, uranium, and impurities such as iron.

Once this eluate is produced, the problem remains of how to recover the uranium from the sulfuric acid eluate and convert the uranium into a useful form such as, for example, sodium diuranate (SDU) or ammonium diuranate (ADU). In the past, a very common method of solving this problem was a solvent extraction (SX) process performed on the sulfuric acid eluate, followed by a stripping step to remove uranium from the solvent, followed by treatment of the strip solution with aqueous sodium hydroxide or aqueous ammonium hydroxide to produce SDU or ADU. However, the use of SX to recover uranium from the sulfuric acid eluates has drawbacks such as solvent degradation, organic losses, and the use of flammable solvents.

It is desired to find a process that does not require treatment with solvents for recovering the uranium from the sulfuric acid eluate. WO 2015/135017 describes a process in which uranium is recovered from a Pregnant Strip Solution (“PSS”, optionally produced by loading a leach solution onto an ion exchange resin and subsequently eluting with sulfuric acid) by loading the PSS onto a separate ion exchange resin that is a chelating resin that contains an amino phosphonic or phosphonic/sulfonic functional groups.

It is desired to provide a process for recovering uranium from sulfuric acid eluate that does not require solvent extraction or the use of chelating ion exchange resins.

The following is a statement of the invention.

A first aspect of the present invention is a process for recovering uranium comprising

-   -   (a) bringing a solution (I) into contact with a resin (I) to         produce a mixture of a solution (II) and a resin (II), wherein         the solution (I) is an aqueous solution that comprises 30 to 200         g/L sulfuric acid and that comprises 1 g/L to 50 g/L uranium,         and wherein the resin (I) is a strong acid cation exchange         resin, and     -   (b) separating the solution (II) from the resin (II).

The following is a brief description of the drawings.

FIG. 1 shows a an embodiment in which solution (I) passes through a bed to resin (I) to produce solution (II) and resin (II).

FIG. 2 shows an embodiment in which further features have been added to the embodiment shown in FIG. 1; the further features added in FIG. 2 provide one method of recovering uranium from resin (II).

FIG. 3 shows an embodiment in which further features have been added to the embodiment shown in FIG. 1; the further features added in FIG. 3 provide a second method of recovering uranium from resin (II).

FIG. 4 shows a flow sheet for and embodiment of Option A as defined below.

FIG. 5 shows a flow sheet for an embodiment of Option B as defined below.

FIG. 6 shows an embodiment of Option B that incorporates a scrubbing step.

FIG. 7 shows uranium loading on a given strong acid cation exchange resin from various solutions containing different concentrations of sulfuric acid and uranium.

FIG. 8 shows uranium loading for various resins at different uranium concentrations at a given concentration of sulfuric acid.

The following is a detailed description of the invention.

As used herein, the following terms have the designated definitions, unless the context clearly indicates otherwise.

As used herein, an aqueous solution is a solution of one or more compound dissolved in a solvent, where the solvent contains water, and where the solution contains 30% or more water by weight.

“Resin” as used herein is a synonym for “polymer.” A “polymer,” as used herein is a relatively large molecule made up of the reaction products of smaller chemical repeat units. Polymers may have structures that are linear, branched, star shaped, looped, hyperbranched, crosslinked, or a combination thereof; polymers may have a single type of repeat unit (“homopolymers”) or they may have more than one type of repeat unit (“copolymers”). Copolymers may have the various types of repeat units arranged randomly, in sequence, in blocks, in other arrangements, or in any mixture or combination thereof. Polymers have weight-average molecular weight of 2,000 or more.

Molecules that can react with each other to form the repeat units of a polymer are known herein as “monomers.” The repeat units so formed are known herein as “polymerized units” of the monomer.

Vinyl monomers have a non-aromatic carbon-carbon double bond that is capable of participating in a free-radical polymerization process. Vinyl monomers have molecular weight of less than 2,000. Vinyl monomers include, for example, styrene, substituted styrenes, dienes, ethylene, ethylene derivatives, and mixtures thereof. Ethylene derivatives include, for example, unsubstituted and substituted versions of the following: vinyl acetate and acrylic monomers. Acrylic monomers are monomers selected from substituted and unsubstituted (meth)acrylonitrile, (meth)acrylic acid, alkyl esters of (meth)acrylic acid, amides of (meth)acrylic acid, vinyl chloride, halogenated alkenes, and mixtures thereof. As used herein, the prefix “(meth)acryl-” means either acryl- or methacryl-. “Substituted” means having at least one attached chemical group such as, for example, alkyl group, alkenyl group, vinyl group, hydroxyl group, alkoxy group, carboxylic acid group, other functional groups, and combinations thereof.

As used herein, vinyl aromatic monomers are vinyl monomers that contain one or more aromatic ring.

A monovinyl monomer is a vinyl monomer that has exactly one non-aromatic carbon-carbon double bond per molecule. A multivinyl monomer is a vinyl monomer that has two or more non-aromatic carbon-carbon double bonds per molecule.

Vinyl monomers are considered to form polymers through a process of vinyl polymerization, in which the carbon-carbon double bonds react with each other to form a polymer chain.

Another type of polymers are those formed by condensation reactions between monomers. For example, phenol and formaldehyde react with each other to form “phenolic resins” or “formophenolic resins.”

A polymer in which 90% or more of the polymerized units, by weight based on the weight of the polymer, are polymerized units of one or more vinyl monomers is a vinyl polymer. A vinyl aromatic polymer is a polymer in which 50% or more of the polymerized units, by weight based on the weight of the polymer, are polymerized units of one or more vinyl aromatic monomer.

A resin is considered herein to be crosslinked if the polymer chain has sufficient branch points to render the polymer not soluble in any solvent. When it is said herein that a polymer is not soluble in a solvent, it means that less than 0.1 gram of the resin will dissolve in 100 grams of the solvent at 25° C.

A resin is considered herein to be a strong acid cation exchange resin (SAC resin) if 50 mole % or more of the polymerized units contain one or more sulfonate group. The sulfonate group may be attached to the monomer prior to polymerization or may be added to the polymerized unit after polymerization. The sulfonate group may be in protonated form, in a neutralized form involving one or more cations other than H⁺, in ionic form, or in a mixture thereof. An SAC resin is said herein to be in “protonated form” if 90 mole % or more of the sulfonate groups attached to the resin are in protonated form.

A resin is considered herein to be a strong base anion exchange resin (SBA resin) if 50 mole % or more of the polymerized units contain one or more quaternary ammonium group. The quaternary ammonium group may be attached to the monomer prior to polymerization or may be added to the polymerized unit after polymerization. The quaternary ammonium group may be in hydroxide form, in a neutralized form involving one or more anions other than OH⁻, in ionic form, or in a mixture thereof.

A resin is considered herein to be a weak base anion exchange resin if 50 mole % or more of the polymerized units contain one or more amine group. The amine groups may be primary, secondary, or tertiary, or a combination thereof. The amine group may be attached to the monomer prior to polymerization or may be added to the polymerized unit after polymerization. The amine group may be free base form, or in a protonated form (i.e., an ammonium group) involving one or more anions or a mixture thereof.

A collection of particles is characterized by the diameters of the particles. If a particle is not spherical, the diameter of the particle is considered to be the diameter of a particle having the same volume as the particle. A collection of particles is characterized herein by the volume-average diameter of the collection.

Resins may be characterized by the average pore diameter, which is measured by the BET method. As used herein, a “gel” resin has average pore diameter of 10 nm or less. As used herein, a “macroporous” resin has average pore diameter of greater than 10 nm.

As used herein, “sulfuric acid” refers to pure H₂SO₄, or to a mixture of H₂SO₄ and water, or to a mixture of H₂SO₄ and sulfur trioxide, or to a mixture of H₂SO₄, water, and sulfur trioxide.

When it is stated herein that a solution contains a particular dissolved ionic species, it is to be understood that the solution may or may not contain one or more ionic species of the same charge as the particular ionic species, and it is to be understood that the solution will contain sufficient ionic species of the charge opposite to the particular ionic species in order to achieve balance of electrical charges.

It is to be understood herein that a statement that a solution contains a particular dissolved compound means that that particular compound dissolves in the solution in the normal way, whether that particular compound dissolves in the form of a complete neutral molecule or whether that particular compound dissolves by forming one or more cation and one or more anion, each of which dissolves separately.

As used herein, an organic solvent is a compound that contains carbon atoms and that is liquid over a temperature range that includes 15° C. to 25° C.

When a ratio is said herein to be X:1 or greater, it is meant that the ratio is Y:1, where Y is greater than or equal to X. For example, if a ratio is said to be 3:1 or greater, that ratio may be 3:1 or 5:1 or 100:1 but may not be 2:1. Similarly, when a ratio is said herein to be W:1 or less, it is meant that the ratio is Z:1, where Z is less than or equal to W. For example, if a ratio is said to be 15:1 or less, that ratio may be 15:1 or 10:1 or 0.1:1 but may not be 20:1.

The process of the present invention involves the use of solution (I). The solution (I) may be formed by any process. Preferably, solution (I) is formed as follows: leaching uranium ore with sulfuric acid to produce an acid leach solution; then passing the acid leach solution through a strong base anion exchange resin to capture [UO₂(SO₄)₃]⁴⁻ anions onto the resin; then removing the uranium from the resin by eluting with sulfuric acid to produce an eluate that contains dissolved sulfuric acid (H₂SO₄) and dissolved UO₂ ²⁺ cations. The eluate may optionally be diluted with water prior to further use. The eluate or the diluted eluate is solution (I). Preferably the eluate is diluted prior to use as solution (I). Preferably, the ratio of dilution water to eluate is, by weight, 0.4:1 or more; more preferably 0.6:1 or more; more preferably 0.8:1 or more. Preferably, the ratio of dilution water to eluate is, by weight, 8:1 or less; more preferably 6:1 or less; more preferably 4:1 or less.

Solution (I) is an aqueous solution that contains uranium and dissolved sulfuric acid. Preferably, the concentration of uranium in solution (I), as elemental uranium, is preferably 1 g/L or more; more preferably 2 g/L or more. Preferably, the concentration of uranium in solution (I), as elemental uranium, is 50 g/L or less; more preferably 20 g/L or less; more preferably 10 g/L or less. Preferably, solution (I) contains dissolved sulfuric acid in an amount of 30 g/L or more; more preferably 40 g/L or more. Preferably, solution (I) contains dissolved sulfuric acid in an amount of 200 g/L or less; more preferably 100 g/L or less. Preferably the pH of solution (I) is 2 or less.

In the process of the present invention, solution (I) is brought into contact with resin (I). Resin (I) is a strong acid cation exchange resin. The mole percent of polymerized units of resin (I) that contains one or more sulfonate groups is 50% or more; preferably 60% or more; more preferably 70% or more; more preferably 80% or more; more preferably 90% or more. Preferably, The mole percent of polymerized units of resin (I) that contains one or more nitrogen-containing groups is 5% or less; more preferably 2% or less; more preferably 1% or less; more preferably zero. Preferably, The mole percent of polymerized units of resin (I) that contains one or more phosphorous-containing groups is 5% or less; more preferably 2% or less; more preferably 1% or less; more preferably zero. Preferably, The mole percent of polymerized units of resin (I) that contains one or more carboxyl groups is 5% or less; more preferably 2% or less; more preferably 1% or less; more preferably zero.

Some examples of commercial resins that are suitable as resin (I) are AMBERJET™ 1600H, AMBERLITE™ 200, AMBERSEP™ 200, AMBERLYST™ 35Wet, and AMBERLYST™ 40Wet; among these three resins, AMBERLYST™ 35Wet is preferred.

Preferably, resin (I) is a vinyl aromatic polymer. Preferred vinyl aromatic monomers are styrene and divinyl benzene. Preferably, the amount of polymerized units of one or more vinyl aromatic monomer is, by weight based on the weight of the polymer, 75% or more; more preferably 90% or more; more preferably 95% or more. Preferably, resin (I) contains polymerized units of one or more multivinyl monomer. Preferably, the amount of polymerized units multivinyl monomer is, by weight based on the weight of resin (I), 2% or more; more preferably 4% or more; more preferably 8% or more; more preferably 10% or more; more preferably 12% or more; more preferably 14% or more. Preferably, the amount of polymerized units multivinyl monomer is, by weight based on the weight of resin (I), 30% or less; more preferably 25% or less. Preferably, resin (I) is made by a process that includes polymerizing a monomer or mixture of monomers that contains one or more monomers that are vinyl aromatic monomers that contain only carbon and hydrogen atoms, and then, after completion of the polymerization, performing one or more chemical reactions to attach one or more sulfonate groups to the aromatic rings in the polymer.

Preferably the resin (I) is in the form of a collection of particles. Preferably the particles contain crosslinked polymer. Preferably the volume-average diameter of the collection of particles is 50 μm or more; more preferably 100 μm or more. Preferably the volume-average diameter of the collection of particles is 1,000 μm or less.

Preferably, before resin (I) is brought into contact with solution (I), the amount of uranium in any form, characterized as grams of elemental uranium per liter of resin, in resin (I) is 5 g/L or less; more preferably 1 g/L or less; more preferably 0.2 g/L or less.

Preferably, before resin (I) is brought into contact with solution (I), resin (I) is in protonated form.

While the present invention is not limited to any particular theory, it is contemplated that when solution (I) is brought into contact with resin (I), some or all of the UO₂ ²⁺ cations in solution (I) will become resident on resin (I), associated with the sulfonate anions attached to the resin (I). The ion exchange reaction of loading uranium on the SAC resin is believed to be the following:

2R—SO₃ ⁻H⁺+UO₂ ²⁺

(R—SO₃ ⁻)₂UO₂ ²⁺+2H⁺

where R is the resin matrix.

Solution (I) and resin (I) are brought into contact with each other to make a mixture. It is contemplated that some alterations in the compositions of solution (I) and resin (I) will take place, for example by transfer of UO₂ ²⁺ cations from solution (I) to resin (I). When the mixture is separated into a liquid portion and a solid portion, the liquid portion will be the altered solution (I), now labeled solution (II); and the solid portion will be the altered resin (I), now labeled resin (II).

It is noted that resin (I) and resin (II) normally contain some water. Each of resin (I) and resin (II) each independently preferably contains water in an amount, by weight based on the total weight of the resin, 1% to 60%.

The steps of bringing solution (I) into contact with resin (I) and then separating solution (II) from resin (II) may be accomplished by any method. A preferred method is to provide a fixed bed of particles of resin (I) and then pass solution (I) through the fixed bed of particles of resin (I). The solution that exits from the fixed bed will be solution (II). Preferably the ratio of the concentration of uranium in solution (I) to the concentration of uranium in solution (II) is 10:1 or more; more preferably 50:1 or more. Preferably, the process of passing solution (I) through the fixed bed of resin (I) is continued until the time when the uranium concentration in solution (II) begins to rise, for example until the ratio of the concentration of uranium in solution (I) to the concentration of uranium in solution (II) falls below 10:1. At that time, the flow of solution (I) is preferably halted. At that time, resin (II) is considered to be “loaded” with UO₂ ²⁺.

Preferably, the amount of dissolved compounds in solution (II) other than H₂SO₄ is, by weight based on the weight of solution (II), 5% or less; more preferably 2% or less; more preferably 1% or less. In some embodiments, solution (II) may be used as a source of sulfuric acid, for example as the sulfuric acid that is mixed with uranium ore to produce an acid leach solution.

Uranium may be recovered from resin (II) by any method It is preferred to recover uranium from resin (II) and convert the uranium to the form of a precipitated diuranate salt. Two preferred methods are herein called “Option A” and “Option B.”

The following is a description of Option A.

Solution (III) is brought into contact with resin (II) to form a mixture. Solution (III) is an aqueous solution that contains dissolved HCl. Preferably the amount of HCl dissolved in solution (III) is, by weight based on the weight of solution (III), 10% or more; more preferably 15% or more. Preferably the amount of HCl dissolved in solution (III) is, by weight based on the weight of solution (III), 30% or less; more preferably 20% or less. Preferably, the total amount of solutes in solution (III) other than HCl is, by weight based on the weight of solution (III), 5% or less; more preferably 2% or less; more preferably 1% or less.

While the present invention is not limited to any particular theory, it is contemplated that when solution (III) is brought into contact with resin (II), some or all of the UO₂ ²⁺ in resin (II) will become converted to UO₂Cl₃ ⁻ and will become dissolved in the water that is present.

Solution (III) and resin(II) are brought into contact with each other to make a mixture. It is contemplated that some alterations in the compositions of solution (III) and resin (II) will take place, for example by conversion of uranium from UO₂ ²⁺ cations resident on resin (II) to UO₂Cl₃ ⁻ dissolved in the water that is present. When the mixture is separated into a liquid portion and a solid portion, the liquid portion will be the altered solution (III), now labeled solution (IV); and the solid portion will be the altered resin (II), now labeled resin (III). It is contemplated that solution (IV) will contain dissolved UO₂Cl₃ ⁻ anions.

The steps of bringing solution (III) into contact with resin (II) and then separating solution (IV) from resin (III) may be accomplished by any method. A preferred method is to provide a fixed bed of particles of resin (II) and then pass solution (III) through the fixed bed of particles of resin (II). The solution that exits from the fixed bed will be solution (IV). Preferably, the previous step of mixing solution (I) with resin (I) is performed by passing solution (I) through a fixed bed of resin (I); then, preferably, the resulting resin (II) stays in the same fixed bed, and solution (III) is then passed through the fixed bed of resin (II). Preferably, the process of passing solution (III) through the fixed bed of resin (II) is continued until the time when the uranium concentration in solution (II) begins to fall. For example, the instantaneous concentration of uranium may be measured as a function of time as solution (IV) exits the fixed bed, and the maximum concentration may be noted. The time may be noted when the ratio of the instantaneous concentration of uranium in solution (IV) as it exits the fixed bed to the maximum concentration is 0.1:1 or lower. At that time, the flow of solution (III) is preferably halted. At that time, resin (II) is considered to be depleted of UO₂ ²⁺, and the depleted resin (II) is known herein as resin (III). It is contemplated that solution (IV) contains dissolved UO₂Cl₃ ⁻ ions.

Preferably, the amount of uranium, as elemental uranium, in resin (III) is 5 gram per liter of resin (g/L) or less; more preferably 1 g/L or less; more preferably 0.2 g/L or less. Preferably, resin (III) could be used as resin (I) in a subsequent performance of the process of the present invention.

In further steps of Option A, solution (IV) is brought into contact with resin (IV). Resin (IV) is a strong base anion exchange resin or a weak base anion exchange resin, preferably a strong base anion exchange resin. When a strong base anion exchange resin is used, the resin is preferably in chloride form. When a weak bas anion exchange resin is used, the resin is preferably in HCl form. Preferably the resin (IV) is in the form of a collection of particles. Preferably the particles contain crosslinked polymer. Preferably the volume-average diameter of the collection of particles is 50 μm or more; more preferably 100 μm or more. Preferably the volume-average diameter of the collection of particles is 1,000 μm or less.

Resin (IV) is preferably a strong base anion exchange resin (SBA resin). Resin (IV) is preferably a gel type resin. Some examples of commercial resins that are suitable as resin (IV) are AMBERLITE™ IRA400, AMBERLITE™ IRA402, AMBERJET™ 4200, AMBERJET™ 4400, AMBERSEP™ 400, DOWEX™ MARATHON™ A, and DOWEX™ MONOSPHERE™ 550A; among these six resins, preferred is AMBERLITE™ IRA400.

Preferably, before resin (IV) is brought into contact with solution (IV), the amount of uranium in any form in resin (IV), characterized as grams of elemental uranium per liter of resin, is 1 g/L or less; more preferably 0.3 g/L or less; more preferably 0.1 g/L or less.

While the present invention is not limited to any particular theory, it is contemplated that when solution (IV) is brought into contact with resin (IV), some or all of the UO₂Cl₃ ⁻ in solution (IV) will become resident on resin (IV), associated with the ammonium groups attached to the resin (IV).

Solution (IV) and resin (IV) are brought into contact with each other to make a mixture. It is contemplated that some alterations in the compositions of solution (IV) and resin (IV) will take place, for example by transfer of UO₂Cl₃ ⁻ anions from solution (IV) to resin (IV). When the mixture is separated into a liquid portion and a solid portion, the liquid portion will be the altered solution (IV), now labeled solution (V); and the solid portion will be the altered resin (IV), now labeled resin (V). It is contemplated that solution (V) contains dissolved HCl. The ion exchange reaction is believed to be the following:

RN⁺Cl⁻+[UO₂Cl₃]

RN⁺[UO₂Cl₃]⁻+Cl⁻

where R represents the resin matrix together with the alkyl groups on the quaternary ammonium group.

It is noted that resin (IV) and resin (V) normally contain some water. Each of resin (IV) and resin (V) each independently preferably contains water in an amount, by weight based on the total weight of the resin, 1% to 60%.

The steps of bringing solution (IV) into contact with resin (IV) and then separating solution (V) from resin (V) may be accomplished by any method. A preferred method is to provide a fixed bed of particles of resin (IV) and then pass solution (IV) through the fixed bed of particles of resin (IV). The solution that exits from the fixed bed will be solution (V). Preferably the ratio of the concentration of uranium in solution (IV) to the concentration of uranium in solution (V) is 10:1 or more; more preferably 50:1 or more. Preferably, the process of passing solution (IV) through the fixed bed of resin (IV) is continued until the time when the uranium concentration in solution (V) begins to rise, for example until the ratio of the concentration of uranium in solution (IV) to the concentration of uranium in solution (V) falls below 10:1. At that time, the flow of solution (IV) is preferably halted. At that time, resin (V) is considered to be “loaded” with UO₂Cl₃ ⁻, associated with the ammonium groups on resin (V).

Preferably, solution (V) is an aqueous solution that contains dissolved HCl. The preferred characteristics of solution (V) are the same as those of solution (III), though the characteristics of the two solutions may be chosen independently. In some embodiments, solution (V) is recycled and used as source for all or part of solution (III).

Preferably, solution (V) qualifies for use as solution (III).

It is contemplated that resin (V) contains uranium in the form of UO₂Cl₃ ⁻. This uranium may be removed from resin (V) by any method. A preferred method is to bring solution (VI) into contact to form a mixture. Preferably, solution (VI) contains water in an amount, by weight based on the weight of solution (VI), 95% or more; more preferably 97% or more; more preferably 99% or more.

While the present invention is not limited to any particular theory, it is contemplated that when solution (VI) is brought into contact with resin (V), some or all of the UO₂Cl₃ ⁻ in resin (V) will become converted to UO₂Cl₂ that is dissolved in the water that is present. The ion exchange reaction is believed to be

RN⁺[UO₂Cl₃]⁻

RN⁺Cl⁻+UO₂ ²⁺+2Cl⁻

where R represents the resin matrix together with the alkyl groups on the ammonium group.

Solution (VI) and resin(V) are brought into contact with each other to make a mixture. It is contemplated that some alterations in the compositions of solution (VI) and resin (V) will take place, for example by conversion of uranium from UO₂Cl₃ ⁻ anions resident on resin (V) to UO₂Cl₂ dissolved in the water that is present. When the mixture is separated into a liquid portion and a solid portion, the liquid portion will be the altered solution (VI), now labeled solution (VII); and the solid portion will be the altered resin (V), now labeled resin (VI). It is contemplated that solution (VII) contains dissolved UO₂Cl₂.

The steps of bringing solution (VI) into contact with resin (V) and then separating solution (VII) from resin (VI) may be accomplished by any method. A preferred method is to provide a fixed bed of particles of resin (V) and then pass solution (VI) through the fixed bed of particles of resin (V). The solution that exits from the fixed bed will be solution (VII). Preferably, the previous step of mixing solution (IV) with resin (IV) was performed by passing solution (IV) through a fixed bed of resin (IV); then, preferably, the resulting resin (V) stays in the same fixed bed, and solution (VI) is then passed through the fixed bed of resin (V). Preferably, the process of passing solution (VI) through the fixed bed of resin (V) is continued until the time when the uranium concentration in solution (II) begins to fall. For example, the instantaneous concentration of uranium may be measured as solution (VII) exits the fixed bed, and the maximum concentration may be noted. The time may be noted when the ratio of the instantaneous concentration of uranium in solution (VII) as it exits the fixed bed to the maximum concentration is 0.1:1 or lower. At that time, the flow of solution (VI) is preferably halted. At that time, resin (V) is considered to be depleted of UO₂Cl₃ ⁻, and the depleted resin (V) is known herein as resin (VI).

Preferably, the amount of uranium, as elemental uranium, in resin (VI) is 1 gram per liter of resin (g/L) or less; more preferably 0.3 g/L or less; more preferably 0.1 g/L or less. Preferably, resin (VI) could be used as resin (IV) in a subsequent performance of the Option A process of the present invention.

Preferably, solution (VII) is brought into contact with a hydroxide to form a mixture, and the corresponding diuranate salt precipitates. The diuranate salt is considered to be a useful form of uranium that is appropriate for various uses. Preferred hydroxides are sodium hydroxide and ammonium hydroxide, which produce precipitates of sodium diuranate (SDU) and ammonium diuranate (ADU), respectively.

The following is a summary of a preferred embodiment of Option A and some of the contemplated ion exchange reactions and expected benefits of performing Option A. Thus, the SAC resin is eluted with HCl, and the uranium is eluted as anionic chloride complex. This eluate passes through a strong or weak base anion exchange resin in the Cl⁻ form where uranium is fixed while HCl comes out and is recovered. Uranium is then eluted from the anion exchanger with water. In this way only a small quantity of chemicals is consumed, which is the HCl that is eluted along with the uranium in the water elution step. From the water eluate, uranium is recovered by precipitation with NaOH or ammonia as SDU or ADU. The flow sheet is shown in FIG. 4.

The following is a description of Option B, for removing uranium from resin (II) and converting the uranium to sodium diuranate.

In Option B, solution (X) is brought into contact with resin (II).

Solution (X) is brought into contact with resin (II) to form a mixture. Solution (X) is an aqueous solution that contains dissolved Na₂SO₄ or dissolved (NH₄)₂SO₄; preferably dissolved Na₂SO₄. Preferably the amount of dissolved Na₂SO₄ or dissolved (NH₄)₂SO₄ in solution (X) is, by weight based on the weight of solution (X), 1% or more; more preferably 2% or more; more preferably 5% or more. Preferably the amount of dissolved Na₂SO₄ or dissolved (NH₄)₂SO₄ in solution (X) is, by weight based on the weight of solution (X), 25% or less; more preferably 20% or less; more preferably 15% or less. Preferably, the total amount of solutes in solution (X) other than Na₂SO₄ or (NH₄)₂SO₄, by weight based on the weight of solution (X), is 5% or less; more preferably 2% or less; more preferably 1% or less.

While the present invention is not limited to any particular theory, it is contemplated that when solution (X) is brought into contact with resin (II), some or all of the UO₂ ²⁺ in resin (II) will become converted to neutral complex or to an anionic complex such as (UO₂[SO₄]₃)⁴⁻ and will become dissolved in the water that is present. It is expected that the SAC resin will not firmly fix the neutral or anionic complex of uranium. It is expected that uranium will elute first, followed by iron, thus achieving a first separation of uranium from iron.

Solution (X) and resin(II) are brought into contact with each other to make a mixture. It is contemplated that some alterations in the compositions of solution (X) and resin (II) will take place, for example by conversion of uranium from UO₂ ²⁺ cations resident on resin (II) to UO₂SO₄ ²⁻ dissolved in the water that is present. When the mixture is separated into a liquid portion and a solid portion, the liquid portion will be the altered solution (X), now labeled solution (XI); and the solid portion will be the altered resin (II), now labeled resin (XI). It is contemplated that solution (XI) will contain dissolved [UO₂(SO₄)₃]²⁻.

The steps of bringing solution (X) into contact with resin (II) and then separating solution (XI) from resin (XI) may be accomplished by any method. A preferred method is to provide a fixed bed of particles of resin (II) and then pass solution (X) through the fixed bed of particles of resin (II). The solution that exits from the fixed bed will be solution (XI). Preferably, the previous step of mixing solution (I) with resin (I) was performed by passing solution (I) through a fixed bed of resin (I); then, preferably, the resulting resin (II) stays in the same fixed bed, and solution (X) is then passed through the fixed bed of resin (II). Preferably, the process of passing solution (X) through the fixed bed of resin (II) is continued until the time when the uranium concentration in solution (XI) begins to fall. For example, the instantaneous concentration of uranium may be measured as solution (XI) exits the fixed bed, and the maximum concentration may be noted. The time may be noted when the ratio of the instantaneous concentration of uranium in solution (XI) as it exits the fixed bed to the maximum concentration is 0.1:1 or lower. At that time, the flow of solution (X) is preferably halted. At that time, resin (II) is considered to be depleted of UO₂ ²⁺, and the depleted resin (II) is known herein as resin (XI). It is contemplated that solution (XI) contains dissolved Na₂SO₄ and dissolved [UO₂(SO₄)₃]²⁻.

Preferably, the amount of uranium, as elemental uranium, in resin (XI) is 1 gram per liter of resin (g/L) or less; more preferably 0.3 g/L or less; more preferably 0.1 g/L or less. Preferably, resin (XI) could be used as resin (I) in a subsequent performance of the process of the present invention.

Preferably, solution (XI) is brought into contact with a hydroxide salt to form a mixture, and the corresponding diuranate salt precipitates. The diuranate salt is considered to be a useful form of uranium that is appropriate for various uses. Preferred hydroxide salts are sodium hydroxide and ammonium hydroxide, which produce, respectively, precipitate of sodium diuranate (SDU) and ammonium diuranate (ADU).

Optionally, after precipitation of diuranate salt, the remaining liquid, which contains dissolved Na₂SO₄, may be used as all or part of solution (X).

Optionally, resin (XI) could be subjected to an additional step in order to remove residual Na₂SO₄ that may be present.

Optionally, Solution (XII) is brought into contact with resin (XI) to form a mixture. Solution (XII) is an aqueous solution that contains dissolved H₂SO₄. Preferably the amount of dissolved H₂SO₄ in solution (XII) is, by weight based on the weight of solution (XII), 1% or more; more preferably 2% or more; more preferably 5% or more. Preferably the amount of dissolved H₂SO₄ in solution (XII) is, by weight based on the weight of solution (XII), 20% or less; more preferably 15% or less; more preferably 10% or less. Preferably, the total amount of solutes in solution (XII) other than H₂SO₄, by weight based on the weight of solution (XII), is 5% or less; more preferably 2% or less; more preferably 1% or less.

Solution (XII) may contain a freshly prepared solution, or solution (XII) may contain material obtained from solution (II), or solution (XII) may contain a mixture thereof.

While the present invention is not limited to any particular theory, it is contemplated that when solution (XII) is brought into contact with resin (XI), some or all of the Na⁺ ions in resin (XI) will become dissolved in the water that is present.

Solution (XII) and resin(XI) are brought into contact with each other to make a mixture. It is contemplated that some alterations in the compositions of solution (XII) and resin (XI) will take place, for example by transfer of Na⁺ ions from resin (XI) to becoming dissolved in the water that is present. When the mixture is separated into a liquid portion and a solid portion, the liquid portion will be the altered solution (XII), now labeled solution (XIII); and the solid portion will be the altered resin (XI), now labeled resin (XII). It is contemplated that solution (XIII) will contain dissolved Na₂SO₄. It is further contemplated that resin (XII) is suitable for use as resin (I).

The steps of bringing solution (XII) into contact with resin (XI) and then separating solution (XIII) from resin (XII) may be accomplished by any method. A preferred method is to provide a fixed bed of particles of resin (XI) and then pass solution (XII) through the fixed bed of particles of resin (II). The solution that exits from the fixed bed will be solution (XIII). Preferably, the previous step of mixing solution (X) with resin (II) was performed by passing solution (X) through a fixed bed of resin (II); then, preferably, the resulting resin (XI) stays in the same fixed bed, and solution (XII) is then passed through the fixed bed of resin (XI). Preferably, the process of passing solution (XII) through the fixed bed of resin (XI) is continued until the time when the sodium concentration in solution (XI) begins to fall. For example, the instantaneous concentration of sodium may be measured as solution (XIII) exits the fixed bed, and the maximum concentration may be noted. The time may be noted when the ratio of the instantaneous concentration of sodium in solution (XIII) as it exits the fixed bed to the maximum concentration is 0.1:1 or lower. At that time, the flow of solution (XII) is preferably halted. At that time, resin (XI) is considered to be depleted of sodium, and the depleted resin (XI) is known herein as resin (XII). It is contemplated that solution (XIII) contains dissolved Na₂SO₄.

Preferably, solution (XIII) is an aqueous solution that contains dissolved Na₂SO₄. The preferred characteristics of solution (XIII) are the same as those of solution (X), though the characteristics of the two solutions may be chosen independently. In some embodiments, solution (XIII) is recycled and used as source for all or part of solution (X).

In order to improve the efficiency of the process, a step can optionally be included where the resin is oversaturated with part of the solution (XI).

In the practice of the present invention, liquid solutions are conveyed from one location to another. In each case, the liquid solutions may be moved by the force of gravity or may be driven by one or more pumps. The liquid solutions may be conveyed through pipes or tubes of any shape of cross section or may be conveyed by any other object capable of conveying liquid from one location to another.

Some specific embodiments of the present invention are shown in the Figures. In FIG. 1, a source 1 supplies solution (I). The source may be any vessel or container. Solution (I) passes through a pipe 2 into a container 3 that holds resin (I) but allows liquid solution to pass through, after making intimate contact with resin (I). Solution (II) exits from container 3 via pipe 4.

FIG. 2 shows the same features as FIG. 1, and FIG. 2 also shows the features of an embodiment of Option A. After solution (I) has passed through container 3 for a time until resin (I) is loaded, the flow of solution (I) is halted. Then, as shown in FIG. 2, the flow of solution (III) is begun, from a source 5. The source may be any vessel or container. Solution (III) passes through a pipe 6 into container 3 that holds resin (II) but allows liquid solution to pass through. Solution (IV) exits from container 3 via pipe 7. Solution (IV) then enters container 8, which contains resin (IV). Solution (IV) passes over resin (IV), and solution (IV) becomes solution (V) and resin (IV) becomes resin (V). Solution (V) exits container 8 via pipe 9. Then the flow of solution (III) is halted, thus also halting the flow of solutions (IV) and (V). Then the flow of solution (VI) is begun, from a source 10. The source may be any vessel or container. Solution (VI) passes through a pipe 11 into container 8. Solution (VI) exits from container 8 via pipe 12. Solution (VI) passes over resin (V), and solution (VI) becomes solution (VII), and resin (V) becomes resin (VI). Solution (VII) exits container 8 via pipe 12.

FIG. 3 shows the same features as FIG. 1, and FIG. 3 also shows the features of an embodiment of Option B. After solution (I) has passed through container 3 for a time until resin (I) is loaded, the flow of solution (I) is halted. Then, as shown in FIG. 3, the flow of solution (X) is begun, from a source 13. The source may be any vessel or container. Solution (X) passes through a pipe 14 into container 3. Solution (X) passes over resin (II), and solution (X) becomse solution (XI) while resin (II) becomes resin (XI). Solution (XI) exits from container 3 via pipe 15.

FIG. 3 also shows an optional further step in Option B, in which, after the flow of solution (X) is halted, the flow of solution (XII) is begun. An additional source supplies solution (XII) to container 3. The source may be any vessel or container. Solution (XII) passes through a pipe 17 into container 3. Solution (XII) passes over resin (XI), and solution (XII) becomes solution (XIII) while resin (XI) becomes resin (XII). Solution (XIII) exits from container 3 via pipe 18.

FIG. 4 shows a flow sheet for an embodiment of Option A.

FIG. 5 shows a flow sheet for an embodiment of Option B. In order to minimize the amount of chemicals consumed, scrubbing of the loaded resin can be done with part of the concentrated eluate (FIG. 6) where the resin is overloaded/saturated with uranium and less with H+ which then can be recovered.

Preferably the process of the present invention does not involve the use of any organic solvent.

Regardless of the specific method used for removing uranium from resin (II), it is contemplated that several advantages arise because the method of the present invention relies upon the use of ion exchange resins and aqueous solutions, without the need for the use of organic solvent. One advantage is that the safety and environmental issues associated with organic solvents are avoided.

Second, compared to SX methods, relatively small amounts of materials are consumed in the process of the present invention. The resins, when saturated, are capable of being regenerated and then re-used. The various solutions that elute from the resins can be put to use within the process of the present invention or else can be recycled for use in other industrial processes. For example, solution (II) is expected to be a solution of sulfuric acid in water, and it is expected that that solution can be recycled to make use of the sulfuric acid.

The following are examples of the present invention.

EXAMPLE 1A Loading the SAC Resin

A solution containing 42 g/L H2SO4 and 2.5 g U/L was allowed to pass through a commercial SAC resin (AMBERLYST™ 35WET, a macroporous strong acid cation exchange resin from the Dow Chemical Company) in the H⁺ form at 1 BV/h (BV=volume of solution/volume of resin) and ambient temperature. After 9 hours (after 9 BV), the effluent concentration was <5 ppm U while the acid was at the feed solution concentration. The resin became saturated after 17 BV where the resin loading was 39 g U/LR (39 g uranium per liter of resin). The resin is considered to be saturated when the ratio of the concentration of uranium in the effluent to the concentration of uranium in solution (I) is 0.95:1 or higher. This is the loading capacity of the head column in a three column merry-go-round configuration (two on loading and one on regeneration).

EXAMPLE 1B Option A

Elution was performed with a 20% HCl solution at 1 BV/h. After 3 BV more than 90% of uranium had been eluted. The eluate was then allowed to pass through a commercial SBA resin (AMBERLITE™ IRA-400, a strong base anion exchange gel resin from the Dow Chemical Company) in Cl⁻ form at 1 BV/h. No uranium was detected in the effluent. Then the resin was eluted with water. After 2 BV of water more than 90% of the uranium had been eluted.

It is contemplated that the lost HCl quantity could be reduced by for example, draining the resins before the water elution.

EXAMPLE 2 Option B

An SAC resin was loaded with uranium as in example 1A. This resin was then eluted with a 10% Na₂SO₄ solution at 1 BV/h. After 4 BV, 90% of the uranium had been eluted from the resin. The resin was subsequently put back to the H form using 2 BV of 5% H2SO4.

It is contemplated that this quantity of H₂SO₄ lost could be decreased by oversaturating (scrubbing) the loaded resin with part of the H₂SO₄ concentrated eluate.

EXAMPLE 3 Comparison of Acid Concentrations

Using AMBERLYST™ 35Wet, the uranium loading capacity was measured as follows. An initial solution of uranium of uranium and sulfuric acid was prepared and a volume V_(S) of this solution was mixed with a given volume of resin V_(R). Uranium concentration of the initial solution is labeled Uo and is reported below in grams of uranium per liter of solution. Three different concentrations of sulfuric acid were used. When equilibrium was established, the uranium concentration was determined and labeled U_(f). The amount of uranium adsorbed on the resin was calculated by _Q=V_(S)*(U₀−U_(f))/V_(R) where Q is the equilibrium loading capacity of the resin. The equilibrium concentration of uranium adsorbed on the resin is reported in grams of uranium per liter of resin (g U/LR). The results are shown in FIG. 7. The lowest concentration of sulfuric acid led to the highest equilibrium loading of uranium on the resin. This result demonstrates the benefit of having the optimum level of sulfuric acid dissolved in solution (I).

EXAMPLE 4 Comparison of Resins

The method of Example 3 was repeated, using 4% sulfuric acid and three different resins. The properties of the resins were as follows. “DVB” is the amount of polymerized units of divinylbenzene in weight % based on the weight of resin.

Resin DVB Number type (%) R1 gel 16.0 R2 gel 8.4 R3 macroporous 16.5

The results are shown in FIG. 8. R3 shows the best uranium loading capacity, followed closely by R1, then followed by R2. This result demonstrates that, as the DVB level increases from 8.4% to 16.5%, the loading capacity also increases.

Overall, the operating capacities of the SAC resins were 20-50 g U/LR (grams of uranium per liter of resin). 

1. A process for recovering uranium comprising (a) bringing a solution (I) into contact with a resin (I) to produce a mixture of a solution (II) and a resin (II), wherein the solution (I) is an aqueous solution that comprises 30 to 200 g/L sulfuric acid and that comprises 1 g/L to 50 g/L uranium, and wherein the resin (I) is a strong acid cation exchange resin, and (b) separating the solution (II) from the resin (II).
 2. The process of claim 1, wherein the solution (I) has been produced by a process comprising bringing uranium ore into contact with sulfuric acid.
 3. The process of claim 1, further comprising (cA) bringing a solution (III) into contact with the resin (II) to form a mixture of a solution (IV) and a resin (III), wherein the solution (III) is an aqueous solution comprising 10% or more HCl by weight, (dA) separating the resin (IV) from the resin (III), (eA) bringing the solution (IV) into contact with a resin (IV), to produce a mixture of a resin (V) and a solution (V), wherein the resin (IV) is a strong base anion exchange resin or a weak base anion exchange resin, and (fA) separating the resin (V) from the solution (V).
 4. The process of claim 3, further comprising (gA) bringing a solution (VI) into contact with the resin (V) to form a mixture of a solution (VII) and a resin (VI), wherein the solution (VI) contains 95% or more water by weight based on the weight of the solution (VI), and (hA) separating the resin (VI) from the solution (VII).
 5. The process of claim 1, further comprising (cB) bringing a solution (X) into contact with the resin (II) to form a mixture of a solution (XI) and a resin (XI), wherein the solution (X) is an aqueous solution comprising dissolved Na₂SO₄ or dissolved (NH₄)₂SO₄, and (dB) separating the resin (XI) from the solution (XI).
 6. The process of claim 5, further comprising (dB) bringing a solution (XII) into contact with the resin (XI), to form a mixture of a solution (XIII) and a resin (XII), wherein the solution (XII) is an aqueous solution comprising dissolved H₂SO₄, and (eB) separating the resin (XII) from the solution (XIII). 